Electronic devices and systems have made a significant contribution towards the advancement of modern society and are utilized in a number of applications to achieve advantageous results. Numerous electronic technologies such as digital computers, calculators, audio devices, video equipment, and telephone systems have facilitated increased productivity and reduced costs in analyzing and communicating data, ideas and trends in most areas of business, science, education and entertainment. These electronic devices are often operated in geographical areas in which catastrophic natural events such as earthquakes occur. Designing electronic equipment with a reasonable level of operational survivability during an earthquake is often very important. For example, a variety of electronic devices are utilized to provide critical emergency services during natural disasters. To be effective the devices typically must remain operational during and after a natural catastrophe. However, accurately testing electrical equipment to ensure it meets earthquake survivability requirements is usually very difficult and often results in undue damage to the equipment being tested.
Communications networking equipment is one example of electronic devices that should have a relatively high degree of earthquake survivability factored into the design. The ability to communicate quickly and reliably in an emergency situation such as an earthquake is vital to many health and safety services. Typically the public communicates with health and safety services by telephone and telephone systems usually rely upon communications networking equipment (e.g., routers) to provide switching and routing of the telephone calls. If the communications networking equipment is not built with enough robustness to operate after an earthquake it becomes very difficult for people to communicate with health and safety services.
The ability of communications network equipment to operate properly after an earthquake is usually dependent upon its ability to withstand forces generated by seismic disturbances. Seismic disturbances usually result in the application of forces that cause the networking equipment to accelerate and move in vertical and horizontal directions. Extreme acceleration changes of the equipment in different directions can cause damage such as connections coming loose, components shaking loose or falling off of equipment framework and buckling, damage or permanent deformation in the framework.
Traditional earthquake survivability testing involves the application of simulated seismic forces to the electronic equipment in accordance with predetermined acceleration time history waveforms. It is important for simulated earthquake tests to be consistent, accurate, repeatable, and applicable to the end-use environment. In order to promote these objectives government and industry organizations have promulgated certain testing standards such as Telcordia (Bellcore) GR-63 criteria. Telcordia (Bellcore) GR-63 specifies Network Equipment-Building System (NEBS) requirements for physical protections in a variety of environmental situations including seismic events.
The Telcordia (Bellcore) GR-63 criteria set forth earthquake survivability testing objectives and requirements. The NEBS requirements indicate that shaking should be applied to the equipment under test (EUT) in each of three orthogonal directions of the EUT. The test requirements indicate the EUT should be subjected to forces that move the EUT in accordance with a synthesized waveform (e.g., acceleration-time history waveform VERTEQII shown in FIG. 1A) by means of a shaker table. Traditional testing systems and methods typically attempt to shake the EUT in accordance with the prescribed motion represented by the synthesized waveform but usually require significant calibration efforts and often not successful at meeting the NEBS requirements.
The Telcordia (Bellcore) GR-63 criteria require the test response spectrum (TRS) for the EUT to be measured and recorded when the EUT is shook. The test response spectrum (TRS) is the shaker table's analyzed acceleration (e.g., in the fast fourier transform (FFT) domain) when reproducing a waveform (e.g., the Bellcore waveform). The NEBS requirements indicate the TRS needs to meet or exceed the required response spectrum (RRS) show in FIG. 1B for the applicable earthquake risk zone in the range from 1.0 to 50 HZ. The NEBS requirements also indicate the TRS is to be calculated using a damping level of 2%.
Most transient vibration testing standards such as the NEBS requirements indicate that the EUT shall be constructed to sustain the waveform testing at prescribed parameters without permanent structural, mechanical or functional damage. NEBS requirements indicate permanent physical damage is defined as deformation of a load bearing element of the equipment being tested (e.g., buckled uprights, deformed bases, cracks and failed anchors or fastening hardware) or a connection failure. Mechanical damage is a dislocation or separation of components (e.g., disengaged circuit cards or modules, opened doors or covers, etc.). The functionality requirements are usually dependent upon the service provided by the equipment and NEBS requirements indicate the EUT shall be constructed to sustain operation without loss of service, replacement of components, manual rebooting, or human intervention immediately before and after each axis of waveform testing.
Meeting earthquake survivability requirements for network telecommunications equipment is usually very difficult and consumes significant resources. Traditional attempts at seismic testing often result in inaccurate results and unnecessary destruction of expensive equipment. For example, traditional testing approaches usually require significant detrimental shaking when calibrating testing equipment after the EUT is placed on a shaker. Calibration is usually required to account for each shaker table's unique response to the dynamic acceleration impacts of the EUT on the shaker table when attempting to reproduce the desired seismic waveform. If the TRS is below the RRS at any point the NEBS standards require the equipment to be retested.
Repetitive shaking associated with calibration and retesting due to failed attempts at meeting the NEBS desired seismic waveform requirements expose the EUT to seismic forces that progressively weaken or otherwise diminish the survivability of the EUT. For example, if the EUT is repetitively subjected to acceleration forces, connections are often gradually shook loose that may have otherwise withstood a shaking in accordance with test requirements (e.g., NEBS requirements) if the simulation forces had been properly applied during an initial attempt (e.g., a TRS is within specified parameters of the RRS). In addition, framework features may become unduly fatigued during repetitive attempts and fail during the final test when they otherwise would not have failed if the initial test was within acceptable parameters.
Another factor affecting the survivability design of the EUT is significantly exceeding acceptable minimum test requirements. There is usually a significant range of acceptable testing results such as withstanding forces greater than some minimum value within a specified percentage (e.g., acceleration forces 30% greater than a RRS). Typically, significant resources are required to design and manufacture electronic equipment that withstands relatively large transient vibration (e.g., seismic) forces. Electronic equipment designed to withstand transient vibrations that exceed an RRS by only a few percentage points (e.g., 3%) typically require less resources to manufacture than electronic equipment that is designed to withstand transient vibrations that exceed an RRS by a significant percentage (e.g., 30%). However, electronic equipment that passes NEBS requirements at values 3% greater than the required accelerations (e.g., test waveform shown in FIG. 1) may fail at values 30% greater. Thus, NEBS requirements may permit application of acceleration forces that exceed minimum requirements by a significant percentage but equipment designed and manufactured to withstand application of such acceleration forces usually requires significant additional resources. Thus, it is often advantageous to have TRS results that are within a few percentage points of the RRS instead of 30% greater. While the Telcordia (Bellcore) GR-63 criteria sets requirements for electronic equipment to satisfy it does not set forth the procedures for testing the equipment without undue testing or commitment of resources.
What is required is a system and method that facilitates earthquake testing adjustments directed at assisting consistent, accurate, and efficient earthquake survivability testing for communications networking equipment with minimal calibration shaking.